This invention relates to gas taps.
Conventional gas taps have comprised a brass or similar metal body provided with a tapered bore in which a similarly shaped plug, also of brass or like metal, has been rotatable, to bring radial ports in the body and plug into register, or take them out of register, to control the flow of gas through the tap. Leakage of gas from the ports along the length of the plug can be avoided because these metals can be given a high degree of finish, and the complementary tapering of plug and bore enable them to be moved relative to one another axially to take up tolerances.
However, brass and similar metals have been increasing in price considerably in recent years, and there is interest in providing a gas tap made from other metals, It is found that when for example aluminium or an alloy thereof is used it is much more difficult to provide satisfactory surface finish and the conventional tapered plug design is impractical to manufacture. Attention has therefore been directed towards the use of cylindrical plungers moved axially in cylindrical bores when "O" rings can be employed to control leakage, and the principal difficulty then is to provide means for fine adjustment of the rate of flow, and hence of the axial position of the plunger without requiring great delicacy of touch in some means for providing the axial displacement.